Submitted by AutoModerator t3_1035nwm in askscience
Weed_O_Whirler t1_j2xrwxj wrote
Reply to comment by Alkaven in Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science by AutoModerator
It doesn't take energy to apply a force. Think of a book sitting on a table. Gravity is pulling the book down (aka, a force pulling down) and the table is pushing up on the book (aka, a force pushing up). And it can just sit there forever. Obviously the table doesn't need energy to do that.
No different than the Sun keeping the Earth in orbit. The energy of the Earth/Sun system stays constant (assuming nothing else in the universe). The force the Sun is providing on the Earth isn't changing its kinetic energy (since kinetic energy only depends on the speed of the object, not its velocity), so conservation of energy doesn't get violated here.
Alkaven t1_j2xxtr4 wrote
Wow okay, thanks! I was totally confounding force and energy. The book example is really helpful.
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